{"course":{"slug":"motion-and-audio","title":"Motion, Sound and Music","url":"https://addaly.com/learn/motion-and-audio","level":"intermediate","track":"create"},"lesson":{"slug":"reverb-and-space","title":"Reverb is information about where","url":"https://addaly.com/learn/motion-and-audio/reverb-and-space","position":58,"of":72,"minutes":10,"answer":"Pre-delay corresponds to the distance of the first reflecting surface at about 34cm per millisecond, and increasing it separates the voice from its own tail.","keyIdea":"Pre-delay corresponds to the distance of the first reflecting surface at about 34cm per millisecond, and increasing it separates the voice from its own tail, which is why a muddy dialogue reverb is fixed with pre-delay before it is fixed with level."},"body":{"format":"markdown","text":"## Reverb is information about where\n\nA completely dry voice sounds like it exists nowhere. That is occasionally what you want (a narrator outside the story, an interior monologue) and almost always wrong for a voice that is supposed to be in a place. Reverb is not decoration; it is the cue that tells a listener the size of the room and the distance to the speaker.\n\nThe physical event it models is straightforward. You speak; the direct sound arrives first. A handful of distinct reflections arrive next, from the nearest surfaces, at times set by their distances. Then the reflections multiply until they become a dense, decaying wash.\n\nEvery reverb control maps to part of that.\n\n## Pre-delay: the control that matters most\n\n**Pre-delay** is the gap between the direct sound and the start of the reverb. It corresponds to the extra distance the first reflection travelled, and at 343 m/s, 1 millisecond is about 34cm.\n\nA 20ms pre-delay implies a reflecting surface roughly 3.4 metres away: the sound went 3.4m out and 3.4m back, arriving about 20ms after the direct. So pre-delay tells the listener how big the room is and how far from the walls the speaker is standing.\n\nIt also has a practical use that has nothing to do with realism: a pre-delay of 20 to 40ms separates the voice from its own tail in time, so the words stay intelligible even with a generous reverb. Zero pre-delay smears the reverb into the consonants and the voice goes mushy. **If a reverb is making the dialogue hard to follow, increase the pre-delay before reducing the level.**\n\n## Decay, early reflections, and the high-cut\n\n**Decay time** (RT60) is how long the tail takes to fall by 60dB. For a voice in a believable interior, 0.4 to 0.8 seconds. A cathedral is 3 to 8 seconds and will swallow speech.\n\n**Early reflections** are the first discrete echoes, and they carry room size more strongly than the tail does. A reverb with strong, well-spaced early reflections and a short tail reads as a small real room; a reverb that is all tail reads as an effect.\n\n**High-frequency damping** is not optional. Air absorbs high frequencies over distance, and soft furnishings absorb them at every bounce, so a real room's reverb tail is duller than its direct sound. A reverb return with full treble sounds artificial and metallic. **Roll the reverb return off above 5 to 8kHz**, and high-pass it below 200 to 300Hz too, which keeps the low end of the mix clear.\n\n## Send, not insert\n\nPut reverb on a **send**: the dry voice goes to the output, a copy goes to a reverb bus, and you mix the wet return underneath. Three reasons.\n\n- The dry signal stays untouched, so intelligibility is preserved and the balance is adjustable at any time.\n- Several sources can share one reverb, which makes them sound as if they are in the same room, which is the point.\n- You can process the return independently: EQ it, compress it, duck it under the dry voice.\n\nAn insert reverb with a wet/dry mix does roughly the same thing for one track and gives up the shared-space benefit.\n\n## Matching a room you already have\n\nThe commonest real task is not \"add atmosphere\" but \"make this studio pickup match the on-location dialogue around it\". The line recorded in a booth has to sit inside a scene recorded in a hallway.\n\nThe approach that works:\n\n1. Find a moment of the location recording with room tone and a reflection you can hear.\n2. Use a **convolution reverb** loaded with an impulse response of a similar space. You can capture one yourself: record a balloon pop or a starter pistol in the room, and the recording *is* the impulse response. Every convolution plugin will load a plain WAV.\n3. Match the pre-delay and decay by ear against the location line, alternating between them.\n4. Match the tone with EQ before reaching for more reverb: a mismatch is usually brightness, not space.\n\nCapturing an impulse response with a balloon costs nothing and is far more accurate than picking a preset called \"Small Room\".\n\n## Amounts\n\nFor dialogue in a visible room, the reverb should be barely noticeable when you solo the voice and clearly missed when you mute it. That test (mute the return and see whether the voice suddenly floats) is the reliable one. If you can point at the reverb, it is too loud for dialogue.\n\nMusic and creative work have no such constraint. Dialogue does, because intelligibility is the job.\n\n## The free path\n\n- **Convolution:** the **IR.lv2** plugin, **x42 zeroconvo**, and Audacity's built-in convolution all load WAV impulse responses free. Large libraries of impulse responses are available under permissive licences, including from the OpenAIR project.\n- **Algorithmic:** **Dragonfly Reverb** is open source, cross-platform, and good. The **Calf** and **LSP** suites include reverbs. **Ardour** ships with a-Reverb.\n- **DaVinci Resolve**'s free Fairlight page includes a full reverb set.\n- **ffmpeg** has `afir` for convolution and `aecho` for crude echoes.\n\n## The limitation\n\nReverb adds a space; it cannot remove one. A recording made in a bad room already contains that room, and adding a nice reverb on top gives you two rooms at once, which sounds worse than either. Dereverberation tools exist and have improved sharply, and they work by estimating and subtracting the room response: with the same class of artefacts as noise reduction, plus a tendency to hollow out the voice.\n\nThe ordering is therefore the same as everywhere else in this module: get it right at the capture stage, because the processing stage is always a negotiation with a loss."},"check":{"question":"A dialogue line with a 0.6 second reverb is hard to follow. What does increasing the pre-delay from 0ms to 30ms do, and why?","options":[{"text":"It shortens the perceived decay time, because the tail now begins later and therefore ends sooner relative to the word.","correct":false,"tempting":"Pre-delay shifts the tail's start; it does not shorten the decay, which continues for its set duration."},{"text":"It reduces the reverb's level at the start of each word, because the reverb send is muted during the pre-delay period.","correct":false,"tempting":"Pre-delay is a delay before the reverb begins, not a gating of the send; the full reverb still arrives."},{"text":"It moves the reverb's onset clear of the consonants, so the direct sound is heard unobscured and the tail arrives after the word is identified.","correct":true},{"text":"It implies a reflecting surface about five metres away rather than immediately adjacent, and the larger implied room is perceived as more open, which is what makes the speech easier to follow in a way that no change in timing alone could achieve.","correct":false,"tempting":"The implied geometry is correct arithmetic, but the intelligibility gain comes from the temporal separation rather than from the perceived room size."}]},"prev":{"slug":"de-essing-and-plosives","title":"Wind, hiss, and why both are placement problems","url":"https://addaly.com/learn/motion-and-audio/de-essing-and-plosives"},"next":{"slug":"ducking-and-beds","title":"Music under speech","url":"https://addaly.com/learn/motion-and-audio/ducking-and-beds"},"authorship":"Founder and series editor: Dr Mustafa Mun. Written by AI models to a written standard. Exam keys checked blind by a second model: 3,665 of 3,666 agreed. Academic review invited.","review":{"status":"Draft, open for academic review"},"cite":"Addaly (2026) 'Reverb is information about where', in Motion, Sound and Music. Edited by M. Mun. Addaly. Available at: https://addaly.com/learn/motion-and-audio/reverb-and-space (Accessed: 13 October 2026).","licence":{"name":"CC BY-NC-SA 4.0","url":"https://creativecommons.org/licenses/by-nc-sa/4.0/"},"reader":{"schema":1,"title":"Reverb is information about where","courseTitle":"Motion, Sound and Music","module":{"index":7,"slug":"shaping-and-mixing-sound","title":"Shaping and mixing sound"},"answer":null,"keyIdea":"Pre-delay corresponds to the distance of the first reflecting surface at about 34cm per millisecond, and increasing it separates the voice from its own tail, which is why a muddy dialogue reverb is fixed with pre-delay before it is fixed with level.","hero":{"kind":"plate","image":null,"alt":null,"caption":null},"blocks":[{"t":"h2","id":"reverb-is-information-about-where","runs":[{"text":"Reverb is information about where"}]},{"t":"p","runs":[{"text":"A completely dry voice sounds like it exists nowhere. That is occasionally what you want (a narrator outside the story, an interior monologue) and almost always wrong for a voice that is supposed to be in a place. Reverb is not decoration; it is the cue that tells a listener the size of the room and the distance to the speaker."}]},{"t":"p","runs":[{"text":"The physical event it models is straightforward. You speak; the direct sound arrives first. A handful of distinct reflections arrive next, from the nearest surfaces, at times set by their distances. Then the reflections multiply until they become a dense, decaying wash."}]},{"t":"p","runs":[{"text":"Every reverb control maps to part of that."}]},{"t":"h2","id":"pre-delay-the-control-that-matters-most","runs":[{"text":"Pre-delay: the control that matters most"}]},{"t":"p","runs":[{"text":"Pre-delay","b":true},{"text":" is the gap between the direct sound and the start of the reverb. It corresponds to the extra distance the first reflection travelled, and at 343 m/s, 1 millisecond is about 34cm."}]},{"t":"p","runs":[{"text":"A 20ms pre-delay implies a reflecting surface roughly 3.4 metres away: the sound went 3.4m out and 3.4m back, arriving about 20ms after the direct. So pre-delay tells the listener how big the room is and how far from the walls the speaker is standing."}]},{"t":"p","runs":[{"text":"It also has a practical use that has nothing to do with realism: a pre-delay of 20 to 40ms separates the voice from its own tail in time, so the words stay intelligible even with a generous reverb. Zero pre-delay smears the reverb into the consonants and the voice goes mushy. "},{"text":"If a reverb is making the dialogue hard to follow, increase the pre-delay before reducing the level.","b":true}]},{"t":"h2","id":"decay-early-reflections-and-the-high-cut","runs":[{"text":"Decay, early reflections, and the high-cut"}]},{"t":"p","runs":[{"text":"Decay time","b":true},{"text":" (RT60) is how long the tail takes to fall by 60dB. For a voice in a believable interior, 0.4 to 0.8 seconds. A cathedral is 3 to 8 seconds and will swallow speech."}]},{"t":"p","runs":[{"text":"Early reflections","b":true},{"text":" are the first discrete echoes, and they carry room size more strongly than the tail does. A reverb with strong, well-spaced early reflections and a short tail reads as a small real room; a reverb that is all tail reads as an effect."}]},{"t":"p","runs":[{"text":"High-frequency damping","b":true},{"text":" is not optional. Air absorbs high frequencies over distance, and soft furnishings absorb them at every bounce, so a real room’s reverb tail is duller than its direct sound. A reverb return with full treble sounds artificial and metallic. "},{"text":"Roll the reverb return off above 5 to 8kHz","b":true},{"text":", and high-pass it below 200 to 300Hz too, which keeps the low end of the mix clear."}]},{"t":"h2","id":"send-not-insert","runs":[{"text":"Send, not insert"}]},{"t":"p","runs":[{"text":"Put reverb on a "},{"text":"send","b":true},{"text":": the dry voice goes to the output, a copy goes to a reverb bus, and you mix the wet return underneath. Three reasons."}]},{"t":"ul","items":[[{"text":"The dry signal stays untouched, so intelligibility is preserved and the balance is adjustable at any time."}],[{"text":"Several sources can share one reverb, which makes them sound as if they are in the same room, which is the point."}],[{"text":"You can process the return independently: EQ it, compress it, duck it under the dry voice."}]]},{"t":"p","runs":[{"text":"An insert reverb with a wet/dry mix does roughly the same thing for one track and gives up the shared-space benefit."}]},{"t":"h2","id":"matching-a-room-you-already-have","runs":[{"text":"Matching a room you already have"}]},{"t":"p","runs":[{"text":"The commonest real task is not “add atmosphere” but “make this studio pickup match the on-location dialogue around it”. The line recorded in a booth has to sit inside a scene recorded in a hallway."}]},{"t":"p","runs":[{"text":"The approach that works:"}]},{"t":"ol","start":1,"items":[[{"text":"Find a moment of the location recording with room tone and a reflection you can hear."}],[{"text":"Use a "},{"text":"convolution reverb","b":true},{"text":" loaded with an impulse response of a similar space. You can capture one yourself: record a balloon pop or a starter pistol in the room, and the recording "},{"text":"is","i":true},{"text":" the impulse response. Every convolution plugin will load a plain WAV."}],[{"text":"Match the pre-delay and decay by ear against the location line, alternating between them."}],[{"text":"Match the tone with EQ before reaching for more reverb: a mismatch is usually brightness, not space."}]]},{"t":"p","runs":[{"text":"Capturing an impulse response with a balloon costs nothing and is far more accurate than picking a preset called “Small Room”."}]},{"t":"h2","id":"amounts","runs":[{"text":"Amounts"}]},{"t":"p","runs":[{"text":"For dialogue in a visible room, the reverb should be barely noticeable when you solo the voice and clearly missed when you mute it. That test (mute the return and see whether the voice suddenly floats) is the reliable one. If you can point at the reverb, it is too loud for dialogue."}]},{"t":"p","runs":[{"text":"Music and creative work have no such constraint. 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"},{"text":"Ardour","b":true},{"text":" ships with a-Reverb."}],[{"text":"DaVinci Resolve","b":true},{"text":"’s free Fairlight page includes a full reverb set."}],[{"text":"ffmpeg","b":true},{"text":" has "},{"text":"afir","code":true},{"text":" for convolution and "},{"text":"aecho","code":true},{"text":" for crude echoes."}]]},{"t":"h2","id":"the-limitation","runs":[{"text":"The limitation"}],"role":"limit"},{"t":"p","runs":[{"text":"Reverb adds a space; it cannot remove one. A recording made in a bad room already contains that room, and adding a nice reverb on top gives you two rooms at once, which sounds worse than either. Dereverberation tools exist and have improved sharply, and they work by estimating and subtracting the room response: with the same class of artefacts as noise reduction, plus a tendency to hollow out the voice."}]},{"t":"p","runs":[{"text":"The ordering is therefore the same as everywhere else in this module: get it right at the capture stage, because the processing stage is always a negotiation with a loss."}]}],"check":{"question":[{"text":"A dialogue line with a 0.6 second reverb is hard to follow. 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